If you haven't given already, or if you can afford to give a little bit more, the easiest way is to text the word "Haiti" to 90999 on your cell phone. This Red Cross-based method of giving is the real deal, according to the U.S. State Department:
For those interested in helping immediately, simply text "HAITI" to "90999" and a donation of $10 will be given automatically to the Red Cross to help with relief efforts, charged to your cell phone.
There are lots of ways to help, and this is a country that really, really needs the help. Their infrastructure was shitty to begin with, and now it's gone. Seeing all the horrible things going on down there is motivation enough to give up $10 that I'll never miss. Hopefully others can do the same.